1,720,954 research outputs found
Uji Aktivitas Antioksidan dan Penetapan Kadar Fenol Total Ekstrak Etanol Herba Apu-Apu (Pistia Stratiotes) dan Fraksi-Fraksinya
No full textRadikal bebas bersifat tidak stabil sehingga akan bereaksi dengan molekul
disekitarnya.Reaksi ini, bila tidak dihentikan akan menimbulkan stress oksidatif
yang dapat menyebabkan kerusakan sel serta berbagai penyakit degeneratif seperti
kanker, jantung, katarak, penuaan dini dan lain-lain. Oleh karena itu, tubuh
memerlukan substansi penting yakni antioksidan yang mampu menangkap radikal
bebas tersebut sehingga senyawa radikal menjadi stabil. Salah satu tumbuhan
yang dapat dimafaatkan sebagai antioksidan yaitu herba apu-apu (Pistia
stratiotes). Tumbuhan apu-apu merupakan salah satu tumbuhan yang memiliki
kandungan kimia fenol yang diduga memilki aktivitas sebagai antioksidan.
Penelitian ini bertujuan untuk mengetahui aktivitas antioksidan dan kadar
fenol total dari ekstrak etanol, fraksi n-heksana, fraksi etil asetat, fraksi etanol air
dari herba apu-apu (Pistia stratiotes). Aktivitas Antioksidan diukur dengan
metode penangkapan radikal bebas DPPH, yaitu dengan mereaksikan larutan
DPPH dengan sampel uji atau pembanding vitamin C yang kemudian diukur
serpannya pada panjang gelombang 517 nm menggunakan spektrofotometri UVVis. Penetapan kadar fenol diukur dengan metode Folin-ciocalteu dengan cara
mereaksikan sampel uji atau standar asam galat dengan reagen Folin- ciocalteu
dan 7,5%, kemudian diukur serapannya pada panjang gelombang 749nm
dengan spektrofotometri UV-Vis.
Hasil penelitian menunjukkan aktivitas antioksidan dari ekstrak etanol,
fraksi n-heksana, fraksi etil asetat dan fraksi etanol air dari herba apu-apu dan
vitamin C secara berturut-turut yaitu 16,675 µg/mL; 29,915 µg/mL; 11,875
µg/mL; 9,090 µg/mL; 3,909 µg/mL. Sedangkan hasil uji penetapan kadar fenol
total dari ekstrak etanol, fraksi n-heksana, fraksi etil asetat dan fraksi etanol air
dari herba apu-apu secara berturut-turut yaitu 231,882 mgGAE/g ekstrak; 197,544
mgGAE/g ekstrak; 276,883 mgGAE/g ekstrak; 350,127 mgGAE/g ekstrak. Hasil
analisis menggunakan ANOVA dan LSD pada aktivitas antioksidan dan kadar
fenol total pada sampel menunjukan nilai signifikansi <0,05 yang artinya terdapat
perbedaan signifikan pada semua kelompok. Fraksi etanol-air herba apu-apu
(Pistia stratiotes) memiliki aktivitas antioksidan dan kadar fenol total tertinggi
pada penelitian ini. Aktivitas antioksidan dan kadar fenol total pada penelitian ini
menunjukan korelasi yang bermakna, dimana kadar fenol yang tinggi maka nilai
rendah sedangkan aktivitas antioksidannya tinggi
Potensi Ekstrak Etanol Herba Apu-Apu (Pistia stratiotes) dan Fraksi-Fraksinya Sebagai Antioksidan Dengan Metode DPPH (Potency of Ethanolic Extract of Pistia stratiotes Herbs and Its Fractions as Antioxidants using DPPH Method)
No full textRadikal bebas berperan penting pada terjadinya kerusakan sel dan penyakit degeneratif seperti penyakit
jantung koroner, stroke, penuaan dini dan lain-lain. Senyawa yang dapat menghambat radikal bebas yaitu
antioksidan. Salah satu tumbuhan yang memiliki kandungan senyawa fenolik tinggi dan bisa menjadi sumber
antioksidan alami yakni apu-apu atau Pistia stratiotes. Penelitian ini dilakukan untuk membuktikan secara
ilmiah adanya aktivitas antioksidan dari ekstrak etanol herba apu-apu (Pistia stratiotes) dan fraksi-fraksinya
dengan metode DPPH. Sampel yang digunakan berupa semua bagian apu-apu (herba apu-apu) yang
didapatkan dari daerah Kecamatan Sumbersari, Kabupaten Jember. Pada penelitian ini digunakan metode
DPPH dengan konsentrasi DPPH sebesar 0,1 mM, waktu inkubasi ekstrak etanol 40 menit, fraksi n- heksana
50 menit, fraksi etil asetat 45 menit, fraksi etanol- air 40 menit, vitamin C 35 menit dan diukur pada pada
panjang gelombang 517 nm. Hasil rata- rata aktivitas antioksidan (IC
50
) yaitu ekstrak etanol herba apu-apu
16,675 µg/mL ± 0,239, fraksi n-heksana 29,915 µg/mL ± 0,156, fraksi etil asetat 11,875 µg/mL ± 0,038,
fraksi etanol-air 9,090 µg/mL ±0,122, dan vitamin C 3,263 µg/mL ± 0,032. Vitamin C sebagai kontrol positif
memiliki aktivitas yang paling tinggi, sedangkan sampel apu-apu yang memiliki aktivitas antioksidan tertinggi
yaitu fraksi etanol-air, dan yang terendah adalah fraksi n- heksana. Dari penelitian ini dapat disimpulkan
bahwa ekstrak etanol herba apu-apu dan fraksi-fraksinya memiliki aktivitas antioksidan, yaitu dari yang tinggi
ke rendah secara berurutan : fraksi etanol-air, fraksi etil asetat, ekstrak etanol herba apu-apu, fraksi n-heksana
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
